A Central Texas homeowner expected a $12,000 AC replacement to make the house more comfortable. Instead, the new Carrier two-stage system left vents rattling, airflow roaring, and indoor humidity stuck at 67%.
That is an especially frustrating outcome in a 20-year-old house where the previous unit had not caused the same moisture problem — and a reminder that an HVAC upgrade should improve comfort and lower bills, not create a costly new headache.
Here's what to know
In a post on Reddit's r/hvacadvice, the homeowner said the home's 20-year-old air conditioner was replaced with a same-size 2-cycle unit for $12,000. The trouble started immediately: The blower was pushing so much air that it caused wind noise across the house and rattled the vents, and the installer later lowered that setting.
Even after that adjustment, the indoor moisture problem remained. "We continue to sit at 67% humidity with the temp set at 73 degrees," the original poster wrote, adding that the thermostat fan was set to Auto and that outdoor relative humidity in Central Texas was only in the 40s.
Several commenters said that is not how a new system should perform. One commenter replied, "Sounds like the blower was left on the factory default highest setting. Call the installer to correct that." Another commenter said their unit had a huge fan-speed range.
For homeowners replacing 20-year-old equipment, Palmetto can help explain HVAC and heat pump options that may reduce energy bills and protect against rising power costs, and since it works as a subscription payment plan with no big upfront payment, it also includes free maintenance to deal with issues like these whenever things are not working as planned.
Palmetto's Comfort Plan network can also help readers find specific options for their home and then connect with vetted installers nearby.
More background
The issue was not an undersized replacement: The homeowner said the new system was the same size as the original unit, yet comfort worsened almost immediately after installation. That suggests the problem may lie in the setup rather than the equipment itself.
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Suggestions in the thread centered on how the system was installed and configured. One commenter questioned whether both stages were actually enabled, saying the first stage should run when appropriate to improve dehumidification. Another warned that even "1/16 inch gaps" between return ducting and the air handler can "drastically affect your return air flow and can lead to high humidity."
Replacing heating and cooling equipment is often one of the better ways to cut utility costs, but a poor installation can leave a homeowner paying for new equipment, dealing with worse humidity, and possibly even needing an unnecessary dehumidifier on top of the original $12,000 expense.
What can be done?
The discussion also narrowed in on airflow checks the installer should perform.
Commenters said the contractor should verify blower airflow against the unit's tonnage, make sure the fan speed is not still set too high, and confirm the CFM and static-pressure settings match what the equipment calls for. Several people in the discussion said dehumidification should improve once airflow is properly adjusted.
Other commenters focused on possible connection and compatibility problems. They said the installer should inspect for duct breaches, recheck the seals where return ducting connects to the air handler, and confirm that the thermostat and air handler are wired to use both stages. One commenter even asked for the model numbers of the thermostat and both the indoor and outdoor units to rule out a mismatch.
If the replacement itself is still ahead of you, Palmetto's Comfort Plan includes $0-down options that can lower heating and cooling costs by up to 50%, plus 12 years of free maintenance. That kind of support can matter when a household is deciding between another repair and a higher-efficiency electric HVAC or heat pump.
Homeowners can also pair solar panels with electric appliances, including efficient HVACs, to push utility bills even lower. EnergySage makes it easy to compare solar options and find the best solar system and installer for a home and budget, and the company says it can help homeowners save up to $10,000 on solar installations.
One commenter wrote: "When set correctly it will provide good dehumidification and cooling. If the fan speed is set too high, more of the units capacity will be used for cooling and less for dehumidification."
Where can I learn more?
These stories dig into the same HVAC problems that show up when an AC upgrade creates new comfort issues. They cover questionable AC add-ons, maintenance steps that affect performance, common airflow mistakes, and ways to pay for efficient replacements.
• In Florida, HVAC pros gave a hard pass to a viral AC saver.
• On TikTok, a homeowner showed that simple drain cleaning can keep AC costs down.
• An HVAC specialist warned that closing your AC vents can raise costs over time.
• Palmetto says its Comfort Plan network helps homeowners finance insulation and HVAC upgrades.
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